Help with routes

Switching our routes file from Rails2 to Rails3 DSl uncovered an odd
situation, of my own making, but I am having some difficultly imagining
how to fix it.

Basically I have a commonplace: user -> user_role (clearance) <- role
type arrangement where:

  has_many :roles, :through => :clearances
  has_many :clearances

  belongs_to :role
  belongs_to :user


  has_many :users, :through => :clearances
  has_many :clearances

What I am trying to do is to link through new_user_role_path(@user).
But I get the following error when I try:

ActionController::RoutingError: No route matches
  {:action=>"new", :controller=>"user_roles"}

The thing is that when I run rake routes I see this:

new_user_role GET /users/:user_id/role/new(.:format)
                      {:controller=>"user_roles", :action=>"new"}

So, I am somewhat nonplussed as to what is going on. I probably am
misunderstanding something basic but from my point of view it seems
that the route that is shown as missing is actually there. Is there
something else I am overlooking?